〔Abstract〕 Objective To explore the effects of Er: YAG laser irrigation technology on smear layer removal and dentin microhardness. Methods A total of 102 ex vivo premolars were selected to amputate the crown, leaving a root length of 13 mm, after mechanical preparation, there were divided into experimental group(3% sodium hypochlorite, 3% NaOCl) and control group(0.9% sodium chloride solution, NS), and received syringe, ultrasound and Er: YAG laser terminal irrigation, which were specifically grouped into NaOCl+syringe, NaOCl+ultrasound, NaOCl+laser, NS+syringe, NS+ultrasound and NS+laser groups(n=17). Scanning electron microscopy(SEM) evaluated smear layer removal from the upper, middle and apical parts of the root. The Vickers microhardness tester measured the microhardness before and after irrigation. Results The NaOCl+laser group had the best effect on removing the root canal smear layer, and the amplitude of reducing the microhardness of dentin was the largest. There was no significant difference in the reduction of microhardness compared with the NaOCl+ultrasonic group(P>0.05). Conclusion Er: YAG laser-activated NaOCl solution improves the clearance of the smear layer and reduced the microhardness of dentin.